Previous technology allows for densitometry of bands diffusing after the termination of electrophoresis. It also yields a single band profile per experiment, and not the time course of dispersion except in those rare cases where a photographic setup allowed one to follow the band in time. But even then, the non-linearity of the photographic response made it difficult to interpret band width data. A recently developed automated gel electrophoresis apparatus with intermittent fluorescence scanning of the migration path solved these problems by providing the band profile while electrophoresis was proceeding. Its width at half-height allows for prediction of band dispersion as a function of migration time and therefore of resolution. The measurement of resolution was used 1) to create a computer program specifying the optimally resolving gel concentration and migration time; and 2) to objectively evaluate the resolving power of separation methods and of the "molecular sieving" capacity of polymers. Availability of the band profile was also used to measure deviations from Gaussian band shape. These were compatible with a model of progressive entanglement of the particle in the gel fiber network. The previous theory of dispersion in gels was modified accordingly. The preparative capacity of the automated apparatus was developed by creating a computer program predicting the electroelution time needed for a selected degree of recovery, and by increasing the load volume capacity of the apparatus from 20 ul to 1.5 ml. The apparatus was also applied to electrophoresis of subcellular-sized particles in polymer solutions. A preparative device for that application was constructed. The provision by the automated technique of large numbers of accurate mobility values served to determine their previously unknown precision, thereby validating the basis of quantitative electrophoresis. The theory of "molecular sieving" was further developed by showing that changes in polymer relaxation times, in addition to a threshold dividing semi-dilute and concentrated regimes, accounted for the triphasic relation between retardation and particle or polymer size.